A century ago, San Francisco was California's biggest city, and at five a.m. on Wednesday, April 18th, the city was starting to wake up. Then, at 5:12, the earth shifted. History professor and former California State Librarian Kevin Starr says there were two jolts, the second one lasting forty seconds.

There was no panic, no noise. "You have a period of silent shock and awe," Starr says. "And people came out on the street, looked to each other, looked around and said; 'What has happened? What has happened?'"

What had happened was that an earthquake -- today estimated at magnitude 7.9 - violently shook the city. Gas lines broke, 60 fires broke out, and the water system failed.

"As devastating as the earthquake was, it did not completely destroy the city," Starr says. "What did the damage were those firestorms and, compounded by the firestorms, was the technique of deliberately dynamiting buildings. In many instances the buildings that were dynamited actually fed the fire."

Today there are fewer than a dozen survivors of the disaster. One of them, Herb Hamrol, 103, and still working part-time at a local supermarket, was three years old when the earthquake hit. "I remember my mother carrying me down the stairs and we slept in the park close by for two nights," he recalls.

The 1906 disaster marked the birth of earthquake science in America. Even as the fires raged for three days, California's governor rounded up 20 of the state's leading scientists. They were challenged to investigate how and why the earth's crust had ruptured with such terrifying violence.

Ross Stein, a geophysicist with the United States Geological Survey says that four years later they produced the Lawson Report, which laid the foundation for much of what is known today about earthquakes.

"Before the 1906 earthquake most scientists thought that an earthquake involved shaking of the ground but not any permanent displacements of the ground," Stein says. "What the Lawson report did was to show us that sudden movement along a fault, a zone of weakness in the earth, produces the earthquake shaking. In addition to producing the shaking, which is what we all feel, it produces permanent displacement of the land."

Author Susanna Hoffman, who has written on the anthropology of disasters, says that people are in a state of denial when they choose to live in a place like California, where earthquakes are always a potential danger.

"Most Californians who've decided to live here decided it's a calculatable risk, it's an okay risk," she says. "People think: 'Well, it's not going to do that much damage, they don't kill that many people.' And actually that is quite true. What kills people is what happens afterwards."

Elke DeMuynck lives directly on top of the Hayward fault, the most dangerous of the seven earthquake faults that criss-cross the San Francisco Bay Area because it is due to snap at any time. Although her house shakes every couple of weeks, she says she doesn't give it a thought or think about the danger on a daily basis.

"Not that I have a false sense of security. But I'd rather live somewhere where the possibility of having an earthquake is, you know, maybe slim-to-none in my lifetime," she says. "But I could be living somewhere like where they're having floods and tornadoes and hurricanes which is a given every year, and I don't know if I could deal with that."

The San Francisco Earthquake and Fire of 1906 is being marked by dozens of commemorative events. On April 18th, the city will mark the anniversary with the traditional wreath-laying at historic Lotta's Fountain, a landmark that survived the disaster. At 5:12 AM there will be a moment of silence, followed by a citywide bell ringing and the traditional singing of the city's anthem, "San Francisco."